Low level windshear is a major aircraft safety hazard, particularly for large swept wing commercial jets. Windshear is a weather condition which results in a rapidly changing airflow over the lift surfaces of the aircraft. Should the forward velocity of the air over the lift surfaces suddenly decrease, the lift will decrease. Hence, an aircraft may experience a forced descent due to the down flowing air mass and also by an apparent loss in forward air speed. Such conditions are typical of a low level windshear.
Ample evidence now exists to substantiate the causal relationship between low altitude windshear (LAWS) and the increase in low altitude aircraft accidents on approach and take-off. It is thus desirable that an on-board aircraft system be available for advanced detection of LAWS giving the pilot at least one minute advanced warning of hazards ahead.
Previously, windshear detection systems have been devised to detect the presence of windshear by using combinations of vertical and horizontal accelerations of the aircraft, air speed and other measurements. The deficiency of that system is that the windshear must be encountered by the aircraft before a warning is given to the flight crew, that is, the systems are reactive in nature. In addition, such systems are unaware of the general atmospheric conditions ahead of the aircraft.
Another windshear detection system that has been used in the past, utilizes a forward looking infrared radiometer to measure the temperature of the air in the extended flight path of the aircraft. This detects the infrared radiation from air and water vapor in front of the aircraft and along its current flight path vector. While this type of system is receiving some use today, it does have some drawbacks. One problem is that at low altitude, the air, especially in a wind shear, is turbulent which makes it difficult to measure a coherent temperature pattern.
Consequently, the development of airborne low level windshear detection system is of considerable value to commercial, corporate and military aircraft.